#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;

ifstream is ("nrtri.in");
ofstream os ("nrtri.out");

int n, x, cnt;
vector <int> v;

int main()
{
    is >> n;
    for (int i = 0; i < n; ++i)
    {
        is >> x;
        v.push_back(x);
    }
    sort(v.begin(), v.end());
    int i, j, k;
    for (k = 2; k < n; k++)
    {
        i = 0;
        j = k-1;
        while (v[i] + v[j] < v[k] && i < j)
        {
            i++;
        }
        cnt += j-i;
    }
    os << cnt;
    is.close();
    os.close();
    return 0;
}